NEO Coordination Centre

Precursor services

Current number of known NEAs:

17854

Current number of NEAs in risk list:

0

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Newsletter

NEOCC Newsletter: March 2018

06 March 2018

The ESA SSA-NEO Coordination Centre has released the March newsletter summarising the most relevant data and events on asteroids and comets approaching the orbit of the Earth. Please, feel free to forward it to potentially interested people.

News

During the first month of 2018 two objects reached a Torino Scale level of 1, and attracted the attention of observers with the goal of collecting additional observations necessary to remove the possible risk. One of them 2017 YZ1, was removed from the risk list within a few days thanks to new observations of various observers, including David Tholen from Hawaii, and our team working in collaboration with the OASI telescope in Brazil.

The other object, 2017 XO2, was harder to remove. By the time it reached Torino Scale 1 it was already quite faint, at magnitude 24, and difficult to observe for most telescopes. There was however another way to get the data needed to clarify the risk: we realised that the Pan-STARRS archive contained a significant amount of images obtained in November and December 2011 that should have covered the area where 2017 XO2 was located, and at that time the object was much brighter, around magnitude 20.

There was a problem however: the uncertainty of the asteroid's position in the sky was huge, many degrees long. Still, we decided to analyse all the dozens of images from one of the many detectors where the object could have been, and after many hours of careful searches we were able to locate the object in the November 5 image set, about 2 sigma away from the expected position.

These images then allowed us to find it in all the other sets from that year, for a total of nine good detections. None of them had been found by the automated Pan-STARRS system because there were only two detections for each night, while automated algorithms need at least three to safely identify a new moving object. Adding these observations to the orbit computation resulted in the immediate exclusion of all possible impact dates for the next century, and the object went directly from Torino Scale level 1 to a complete removal from our risk list.

Animation of two images of 2017 XO2 taken on 2011 November 25 by the Pan-STARRS telescope. The two images were exposed approximately 18 minutes apart, and the object is visible in the top half of the image. Credit: Pan-STARRS

News

A few weeks ago the Pan-STARRS survey discovered a new NEO, temporarily identified as P10G8tt and then formally designated 2018 AM12. Follow-up observations over the next few days allowed the determination of its distance, and consequently its absolute magnitude, which turned out to be roughly 21.4. This brightness should correspond to a diameter between about 150 m and 300 m, depending on the unknown albedo of the object's surface.

A few days later one of our collaborators, Erwin Schwab, was using the 0.8-metre Schmidt telescope in Calar Alto, Spain, to collect observations of the asteroid, while he noticed that the object was an extremely fast rotator, with a rotation period of roughly 12.5 minutes. He collected data over about two hours, which resulted in the lightcurve shown in the figure below.

This fast period is unusual for an object of this size, since it is known that almost all objects larger than ~200 m tend to have periods longer than 2 hours (the so-called spin barrier).

The object is now approximately of magnitude 20, but it is getting fainter quite fast. Obtaining a taxonomical classification of it, or any other proxy for its albedo, would allow us to determine its actual size more accurately. If the object turns out to be larger than the spin barrier, it would be interesting to investigate its physical properties in greater detail.

The results of these observation have been submitted for publication to the Minor Planet Bulletin.

Lightcurve of 2018 AM12 obtained on 2018 January 16 with the Calar Alto Schmidt telescope, phased with the detected rotational period of 12.64 minutes. Credit: E. Schwab

Close Approach Fact Sheet

NEOCC Close Approach Fact Sheet: 2012 TC4

06 October 2017

The ESA SSA-NEO Coordination Centre has released a Close Approach Fact Sheet (CAFS) for asteroid 2012 TC4, passing by Earth on 12 October. Please, feel free to forward it to potentially interested people.